Valve train with variable valve actuation

ABSTRACT

A valve train assembly includes valves having a valve stem; a main camshaft having main cams corresponding to the valves; main rocker arms corresponding to the valves; an auxiliary cam arranged on the main camshaft; at an auxiliary cam follower following the auxiliary cam, the auxiliary cam follower being movably arranged on a main rocker arm between a first and second position; and a latch on a main rocker arm for locking the auxiliary cam follower in the first position. A rotatable control rod controlling the latch is between the first and the second positions. The control rod includes a transmission element configured to convert torque in the control rod into a control force to control movement of the latch.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a U.S. National Stage Application under 35 U.S.C. § 371 of International Application No. PCT/EP2016/079754 filed on Dec. 5, 2016, and claims benefit to British Patent Application Nos. GB 1521380.4 filed on Dec. 3, 2015 and GB 1522141.9 filed on Dec. 15, 2015. The International Application was published in English on Jun. 8, 2017 as WO 2017/093565 A1 under PCT Article 21(2).

FIELD

The present invention relates to a valve train with a variable valve actuation.

BACKGROUND

A valve train assembly can include: a number of valves each having a valve stem; at least one main camshaft with a number of main cams, at least one main cam corresponding to each valve; a number of main rocker arms, each main rocker arm corresponding to a valve and having a valve stem actuation portion, a pivot axis parallel to the main cam shaft and a main cam follower for following the corresponding main cam, wherein the valve stem actuation portion, the pivot axis and the main cam follower are arranged along the length of the main rocker arm and at a distance from each other; at least one auxiliary cam arranged on the main camshaft; at least one auxiliary cam follower for each auxiliary cam and for following said auxiliary cam, wherein each auxiliary cam follower is movable arranged on one of the main rocker arms between a first and a second position; and a latch arranged on the respective main rocker arm for locking the auxiliary cam follower in the first position.

By way of example, a valve train assembly is described in the earlier patent application PCT/EP2015/061768 of the applicant.

In this valve train, a latch is controlled by an auxiliary camshaft with a selector cam, which is in contact with the latch. The control force exerted by the selector cam on the latch is in radial direction to the auxiliary camshaft. As a result, it is required, that the auxiliary camshaft is positioned close to the rocker arms, in which the latches are mounted.

If this valve train assembly is to be mounted on an existing cylinder head of a combustion engine, the inventors have recognized that modifications need to be done to the cylinder head and even the cylinder head might have to be redesigned to provide space for the auxiliary camshaft.

Also, the auxiliary camshaft needs to be actuated to put the latches in the correct positions depending on the conditions of the engine. This actuation of the auxiliary camshaft is typically performed by an electric motor or the like, which needs to be coupled to the auxiliary camshaft. With the above valve train, the inventors have recognized that coupling of a motor to the camshaft proves difficult and requires further modification of the cylinder head, as the auxiliary camshaft is typically positioned deep in the cylinder head, directly adjacent of the rocker arms.

So, with the above-described valve train the inventors have recognized that substantial modifications need to be made to the cylinder head of an existing combustion engine, when such a valve train is to be mounted to cylinder head.

SUMMARY

In an embodiment, the present invention provides a valve train assembly that includes a plurality of valves each having a valve stem; at least one main camshaft with a plurality of main cams—at least one main cam corresponding to each of the valves; a plurality of main rocker arms—each of the main rocker arms corresponding to one of the valves and having a valve stem actuation portion, a pivot axis parallel to the at least one main cam shaft and a main cam follower for following the corresponding one of the main cams, the valve stem actuation portion, the pivot axis and the main cam follower being arranged along a length of a corresponding one of the main rocker arms and at a distance from each other; at least one auxiliary cam arranged on the at least one main camshaft; at least one auxiliary cam follower for each of the at least one auxiliary cam and for following the at least one auxiliary cam, the respective at least one auxiliary cam follower being movably arranged on one of the main rocker arms between a first position and a second position; and a latch arranged on a respective one of the main rocker arms for locking the at least one auxiliary cam follower in the first position. At least one rotatable control rod for controlling the respective latch between the first position and the second position. The at least one control rod includes for the respective latch a transmission element, the transmission element configured to convert torque in the at least one control rod into a control force tangential to the at least one control rod to control movement of the latch between the first and second position.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. All features described and/or illustrated herein can be used alone or combined in different combinations in embodiments of the invention. The features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following:

FIG. 1 illustrates an enlarged perspective view partially in cross section of a valve train assembly;

FIG. 2 illustrates a partial perspective view of a combination according to the invention;

FIGS. 3A and 3B illustrate a first embodiment of the valve train assembly according to the invention;

FIGS. 4A and 4B illustrates a second embodiment of the valve train assembly according to the invention;

FIG. 5 illustrates an embodiment of cast metal rocker arm for the valve train assembly of the invention;

FIG. 6 illustrates a perspective view of a part of a third embodiment of the valve train assembly according to the invention; and

FIGS. 7A and 7B illustrate the third embodiment in cross sectional view in two different positions.

DETAILED DESCRIPTION

Embodiments of the invention reduce or even remove the above-mentioned disadvantages of valve train assemblies.

Embodiments reduce or remove those disadvantages by providing a valve train assembly having at least one rotatable control rod for controlling the latches between the first and second position, wherein the at least one control rod includes for each latch a transmission element, which transmission element converts the torque in the at least one control rod into a control force tangential to the control rod to control movement of the latch between the first and second position.

With the valve train according to embodiments of the invention, a transmission element is provided for each latch, such that a control force tangential to the control rod can be exerted on to the latch. As a result, the distance between the control rod and the latches, arranged in the rocker arms, can be larger and there is no need to have the control rod in line with the latches, as is the case with known valve train assemblies. Accordingly, the control rod can be positioned more freely within the cylinder head, such that the number of modifications of the cylinder head can be substantially reduced or even be prevented.

The main rocker arm can be manufactured from sheet steel, but more preferably, the rocker arm is a cast metal object. By casting the rocker arm, the manufacturing costs for a large number of rocker arm can be kept low as a limited finishing operations are required. Furthermore, a cast metal rocker arm is able to better transfer the forces from the cam shafts and valves, enabling to minimize the weight of the rocker arms.

While cast metal rocker arms are preferred for the valve train assembly of the invention, such cast metal rocker arms could also be applied on the valve train assembly from PCT/EP2015/061768.

In a preferred embodiment of the valve train assembly according to the invention, the transmission element is an elongate element arranged with one end to the control rod and wherein the other end of the elongate element engages the latch. Preferably, the control rod extends substantially in radial direction.

The elongate element, such as a small beam, provides a lever, with which the rotation of the control rod is converted into a tangential force, with which the latch can be controlled between the first and second position. This allows for a position of the control rod at a distance from the latches and rocker arms, in which the latches are arranged. This position of the control rod can be selected more freely and the elongate elements can be shaped such that the existing design and components of the cylinder head are circumvented by the elongate elements and the torque of the control rod is transferred to the latches.

In a further embodiment of the valve train assembly according to the invention a substantially U-shaped or R-shaped leaf spring is arranged between the other end of the elongate element and the latch, wherein the leaf spring is arranged with one free end to the latch.

With the known valve train assembly, a compliance spring in the form of a coil spring is arranged on the latch pin. This compliance spring ensures that the control cam can be rotated from a position in which the latch is unlocked to a position for locking the latch position, even when the latch is not yet registered with a latch opening.

The substantially U-shaped or R-shaped leaf spring provides the same compliance spring function, while a U-shaped or R-shaped leaf spring is more easily mounted to the latch and provides a simple design, than the coil spring used in the known valve train assembly. Such a leaf spring could also be used in the known valve train assembly, where at least one auxiliary camshaft with a selector cam for each latch is provided to control said latch.

Another preferred embodiment of the valve train assembly according to the invention further comprises a camshaft carrier for accommodating the main camshaft, wherein the transmission element comprises a control cam arranged on the control rod and a curved leaf spring arranged between the control cam and latch, wherein one free end of the curved spring leaf is arranged to the camshaft carrier.

With the known valve train assembly, the auxiliary camshaft needs to be positioned close or adjacent the rocker arms, which are provided with the latches. With the invention, the control rod with the control cams can be placed more freely in the cylinder head, for example on top of the mounting of the main camshaft. By using transmission elements, which are in this embodiment curved leaf springs, the torque in the control rod is converted via the control cams and the curved lead springs into a control force for operating the latches. A free end of the curved leaf spring needs to be fixedly mounted, in particular to the camshaft carrier, such that the control cam can tilt the curved spring around the fixation point, while the other free end of the spring can act on the latch to control it between the first and second position. On top of that, the curved leaf spring also acts as a compliance spring, such that the latch no longer needs to be provided with such an additional compliance spring.

Preferably, the curved leaf spring is substantially C-shaped, wherein the control cam engages on the curved leaf spring at a distance from the attachment of the one free end to the camshaft carrier and wherein the other free end of the curved leaf spring engages the latch.

In yet another embodiment of the valve train assembly according to the invention, the control rod is rotatable between two angles and the control rod is provided with bends to accommodate components of a cylinder head on which the valve train assembly is to be mounted.

As the control rod only needs to rotate between two angles to control the latch between two positions, and the control rod does not need to be rotated over a full revolution, the control rod can be provided with bends in order to circumvent components or the shape of the cylinder head. For example it is possible to circumvent a timing wheel of the timing belt, by providing a U-shaped bend in the control rod.

In still another embodiment of the valve train assembly according to the invention, the curved leaf spring is being bent from a M-shaped starting shape, wherein the leaf spring comprises a bridge portion from which three legs extend parallel to each other, wherein the two outer legs are arranged to the camshaft carrier and wherein the free end of the middle leg engages the latch.

This curved leaf spring is easily bent out of a flat piece of spring steel having an M-shape. As both outer legs are attached to the camshaft carrier, which is typically arranged to the cylinder head, a pivot support is provided for the middle leg. Furthermore, as the middle leg is supported on both sides by the attached outer legs, the control cam will cause the middle leg to pivot in a defined and predictable manner to control the latch.

Preferably, the outer legs of the curved leaf spring extend on opposite sides of control cam. This provides for symmetry, such that the force exerted by the control cam is evenly distributed along the leaf spring and that torsions in the leaf spring is minimized.

Furthermore, it is preferred if the outer legs are provided with U-shaped free ends. The U-shaped free ends provide for additional spring action and contribute to the compliance spring function enabling the control cam to be rotated at any time, irrespective of alignment of auxiliary and main camshaft.

In yet another embodiment of the valve train assembly according to the invention, the latch comprises a pin movable in the length of the main rocker arm, wherein one end of the pin is engagable on the auxiliary rocker arm and wherein the pin is urged with the other end in contact with the transmission element.

The control force, which is tangential to the control rod and is generated from a torque in the control rod via the transmission element, will be substantially coaxial with the pin of the latch.

The invention also relates to a combination of a cylinder head for a combustion engine and a valve train assembly according to the invention, wherein the valve train assembly is mounted on the cylinder head.

An embodiment of the combination according to the invention further comprises an actuator, such as an electric motor, arranged on a side of the cylinder head, which actuator is coupled to the control rod for rotating said control rod.

Because the control rod can be positioned more freely within the cylinder head, the position of the actuator, which is typically mounted on the outside of the cylinder head, can also be chosen more freely.

Preferably the actuator is coupled to an end of the control rod or the actuator is coupled to a midsection of the control rod via a worm drive.

These and other features of the invention will be elucidated in conjunction with the accompanying drawings.

FIG. 1 shows an enlarged perspective view partially in cross section of a valve train assembly 1 according to patent application PCT/EP2015/061768 of the applicant. In FIG. 1, a main cam shaft 20 is depicted having main cams 21, 22 and auxiliary cams 23, 24. The main rocker arms 6 rests with one end on a valve stem 4 to operate the corresponding valve.

Each main rocker arm 6 has an auxiliary rocker arm 25 pivotable around an axle 26. A spring 27 is arranged around the axle 26 and attached to the auxiliary rocker arm 25 to urge the arm 25 upwardly. The auxiliary rocker arm 25 is furthermore provided with an auxiliary cam follower 28, which follows the profile of the auxiliary cam 23, while a main cam follower 9 is provided to follow the profile of the main cams 21, 22.

The latch 12 operated by the selector cam 14 on the auxiliary cam shaft 16 has a pin 29, which is movable in the length of the main rocker arm 6. Springs 30 urges the pin 29 against the selector cam 14. The other end of the pin can be shifted into the auxiliary rocker arm 25 to lock the auxiliary rocker arm 25 to the main rocker arm 6. The springs 32 arranged between the pin 29 and the selector cam 14 ensure that the selector cam 14 can be rotated at any time, even when the auxiliary rocker arm is 25 is not yet aligned with the main rocker arm 6.

As will be clear, the selector cam 14 exerts a control force F on the latch 29, which force F is radial to the auxiliary cam shaft 16. This requires for the auxiliary cam shaft 16 to be close to the rocker arm 6, 7 and for the axis of the auxiliary cam shaft 16 to be coplanar with the axis of the latch 29.

FIG. 2 shows a partial perspective view of a combination 50 according to the invention. The combination 50 has a cylinder head 51 with inlet openings 52 and outlet openings 53. A main cam shaft 54 is provided having main cams 55 and auxiliary cams 56, similar to the embodiment of FIG. 1.

The main cam shaft 54 is mounted to a camshaft carrier 57 by brackets 58. These brackets 58 also comprise through holes along which a control rod 59 extends. The control rod 59 has elongate elements 60 for controlling latches, as explained in detail with FIGS. 3A and 3B.

The control rod 59 is provided with a U-shaped bend portion 61 to circumvent a timing belt wheel 62. Furthermore the control rod 59 is coupled to an electric motor 63, which is arranged on the outside of the cylinder head 51.

FIGS. 3A and 3B show a first embodiment of the valve train 70 assembly according to the invention. Similar to the valve train assembly 1 of FIG. 1, this valve train assembly 70 has a main rocker arm 71, which is with one end supported on a fixed pivot 72 and with the other end on a valve stem 73. The main rocker arm 71 has an auxiliary rocker arm 74 with an auxiliary cam follower 75 hingedly arranged to the main rocker arm 71. The auxiliary cam follower 74 is in contact with an auxiliary cam 56 on the camshaft 54.

A latch pin 76 is arranged in the main rocker arm 71 to lock the auxiliary rocker arm 74 (as shown in FIG. 3A) or in unlocked position (as shown in FIG. 3B).

The latch pin 76 is operated by the control rod 59 and the elongate element 60, which is in contact with a U-shaped leave spring 77. This U-shaped leave spring 77 is arranged with one free end 78 to the latch pin 76. This U-shaped spring 77 provides the same functionality as the spring 32 of the embodiment shown in FIG. 1.

By using an elongate element 60, the torque in the control rod 59 can be converted to a tangential force F, which is arranged at a radius R from the control rod 59. As a result, the control rod 59 can be positioned more freely in the cylinder head and does not need to be adjacent the main rocker arm 71, such as in the embodiment shown in FIG. 1.

FIGS. 4A and 4B show a second embodiment 80 of the valve train assembly according to the invention. This embodiment 80 is largely similar to the embodiment 70 and corresponding element are provided with the same reference signs.

Instead of a control rod 59 with elongate elements 60 and a U-shaped spring 77, this embodiment 80 is provided with a control rod 81, on which control cams 82 are arranged. The cam 82 is in contact with a curved leaf spring 83, which is arranged with one end 84 to the cylinder head 85, for example to the camshaft carrier.

The curved leaf spring 83 has another free end 86, which can be brought in contact with the latch pin 76. In FIG. 4A, the lobe of the cam 82 contacts the leaf spring 83, such that the other free end 86 is pressed against the latch 76 coupling the auxiliary rocker arm 74 with the main rocker arm 71.

When the control rod 81 is rotated, the lobe of the cam 82 is brought out of contact with the curved leaf spring 83, such that the latch 76 can be moved by the spring 87 to a position, in which the auxiliary rocker arm 74 can freely rotate in the main rocker arm 71 (see FIG. 4B)

FIG. 5 shows an embodiment of cast metal rocker arm 90 for the valve train assembly of the invention. This rocker arm 90 has a cast metal main rocker arm 91, in which an auxiliary rocker arm 92 is arranged pivotable around the pivot axis 93.

The main rocker arm 91 is provided with two cam followers 94, while the auxiliary rocker arm is provided with a single cam follower 95. A spring 96 urges the auxiliary rocker arm 92 into the shown position, while a latch pin 97 enables locking or unlocking of the auxiliary rocker arm 92 to the main rocker arm 91.

The latch pin 97 is provided with an R-shaped leave spring 98, which ensures that a force can be applied to the latch 97, even when the auxiliary rocker arm is 92 is not yet aligned with the main rocker arm 91.

This rocker arm 90 cannot only be applied to the valve train assembly according to the invention, but also to the valve train assembly according to the patent application PCT/EP2015/061768.

FIGS. 6, 7A and 7B show a third embodiment 100 of a valve train assembly according to the invention. This embodiment 100 is partially similar to the second embodiment 80 and corresponding parts are designated with the same reference signs.

FIG. 6 shows schematically a control rod 101 with a control cam 102, which actuates a leaf spring 103. In FIG. 6, two leaf springs 103 are shown besides each other with the control rod 101 cut away for one of the leaf springs 103.

Each leaf spring 103 is arranged to a part 104 of the cylinder head on which the valve train assembly 100 is arranged. Each leaf spring 103 has an M-shaped starting shape having a bridge portion 105 from which three legs 106, 107, 108 extend. The outer legs 106, 108 are bent into a U-shape, such that the free ends of the outer legs 106, 108 are perpendicular to the bridge part 105. The free ends of the outer legs 106, 108 are attached to the part 104.

The middle leg 107 provides a lever, which is actuated by the control cam 102 and with which the latch pin 76 is actuated. The free end of the middle leg 107 is folded into a U-shape to provide an additional spring, which can act as a compliance spring.

As the middle leg 107 is attached to the part 104 of the cylinder head via both outer legs 106, 108 via the U-shaped ends, the middle leg 107 can pivot along a resiliently suspended pivot axis, which contributes to the compliance spring function: So even when the auxiliary rocker arm is 74 is not yet aligned with the main rocker arm 71, the control cam 102 can be rotated to the position shown in FIG. 7A, which is facilitated by the deformation of the U-shape in the outer legs 106, 108, the U-shape in the middle leg 107 as well as bending of the middle leg 107. As soon as the auxiliary rocker arm 74 and main rocker arm 71 align, the latch pin 76 can be shifted to lock both rocker arms 71, 74 to each other.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments.

The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C. 

1: A valve train assembly comprising: a plurality of valves each having a valve stem; at least one main camshaft with a plurality of main cams, at least one main cam corresponding to each of the valves; a plurality of main rocker arms, each of the main rocker arms corresponding to one of the valves and having a valve stem actuation portion, a pivot axis parallel to the at least one main cam shaft and a main cam follower for following the corresponding one of the main cams, wherein the valve stem actuation portion, the pivot axis and the main cam follower are arranged along a length of a corresponding one of the main rocker arms and at a distance from each other; at least one auxiliary cam arranged on the at least one main camshaft; at least one auxiliary cam follower for each of the at least one auxiliary cam and for following the at least one auxiliary cam, wherein the respective at least one auxiliary cam follower is movably arranged on one of the main rocker arms between a first position and a second position; a latch arranged on a respective one of the main rocker arms for locking the at least one auxiliary cam follower in the first position, and at least one rotatable control rod for controlling the respective latch between the first position and the second position, and wherein the at least one control rod comprises for the respective latch a transmission element, the transmission element configured to convert torque in the at least one control rod into a control force tangential to the at least one control rod to control movement of the latch between the first and second position. 2: The valve train assembly according to claim 1, wherein the transmission element is an elongate element arranged with one end to the at least one control rod, and wherein an other end of the elongate element engages the latch. 3: The valve train assembly according to claim 2, wherein a substantially U-shaped or R-shaped leaf spring is arranged between the other end of the elongate element and the latch, and wherein the leaf spring is arranged with one free end to the latch. 4: The valve train assembly according to claim 1, further comprising a camshaft carrier for accommodating the at least one main camshaft, wherein the transmission element comprises a control cam arranged on the at least one control rod and a curved leaf spring arranged between the control cam and the latch, and wherein one free end of the curved spring leaf is arranged to the camshaft carrier. 5: The valve train assembly according to claim 4, wherein the curved leaf spring is substantially C-shaped, wherein the control cam engages on the curved leaf spring at a distance from the attachment of the one free end to the camshaft carrier, and wherein the other free end of the curved leaf spring engages the latch. 6: The valve train assembly according to claim 4, wherein the curved leaf spring is bent from a M-shaped starting shape, wherein the leaf spring comprises a bridge portion from which three legs extend parallel to each other, wherein two outer legs of the three legs are arranged to the camshaft carrier, and wherein the free end of a middle leg of the three legs engages the latch. 7: The valve train assembly according to claim 6, wherein the two outer legs of the curved leaf spring extend on opposite sides of the control cam. 8: The valve train assembly according to claim 6, wherein the two outer legs are provided with U-shaped free ends. 9: The valve train assembly according to claim 1, wherein the at least one control rod is rotatable between two angles, and wherein the at least one control rod is provided with bends to accommodate components of a cylinder head on which the valve train assembly is to be mounted. 10: The valve train assembly according to claim 1, wherein the latch comprises a pin movable in a length of a corresponding one of the main rocker arms, wherein one end of the pin is engagable on an auxiliary rocker arm, and wherein the pin is arranged with its other end in contact with the transmission element. 11: A system comprising a cylinder head for a combustion engine and the valve train assembly according to claim 1, wherein the valve train assembly is mounted on the cylinder head. 12: The system according to claim 11, further comprising an actuator arranged on a side of the cylinder head, the actuator being coupled to the at least one control rod for rotating the at least one control rod. 13: The system according to claim 12, wherein the actuator is coupled to an end of the at least one control rod. 14: The system according to claim 12, wherein the actuator is coupled to a midsection of the at least one control rod via a worm drive.
 15. The system according to claim 12, wherein the actuator is an electric motor. 